In the field of lithography for exposing a circuit pattern in the process of manufacturing a semiconductor (LSI), electron beam exposure technology is being utilized. Specifically, in the semiconductor lithography technology, photochemical process technology (photolithography) has been mainly used, in which a mask, serving as an original pattern, is generally created by an electron beam exposure device and the mask image is optically transferred onto a semiconductor substrate (wafer).
Electron beam exposure systems have been developed, starting from a method called
one-stroke sketch (a picture drawn with a single stroke of the brush) with narrowly-focused electron beams, to a variable rectangular method, a method called character projection (CP) in which one-shot exposure of several square microns is performed with a micro mask, and so on.
In such an electron beam exposure device, an electron gun which emits an electron beam is significant. In Non-Patent Document 1, for example, a method of holding and a method of heating an electron gun cathode, which is of a type called Vogel mount type, are used. The electron gun in this document is configured such that an electron gun cathode, which is an electron generation source, is sandwiched by pyrolytic graphite (PG) members functioning as heating elements on respective sides and is further pressed and held, on the respective sides, by metal springs. The heating state of the PG members is controlled with electric current which is caused to flow in the PG members, and thermoelectron emission conditions are obtained. This conventional electron gun will be described with reference to FIG. 13.
This electron gun cathode is composed of a single crystal chip 801 of LaB6 or CeB6 having conductivity and a work function for generating electrons; i.e. about 2.6 eV, and two pyrolytic graphite members 802a and 802b, which are cut with a plane vertical to the C-axis direction, sandwiching the chip 801. This structure is further held by metal supports 803a and 803b and further urged by components 804a and 804b forming springs at an appropriate pressure. The force of the spring is adjusted by rotating clamping screws 806a and 806b to vary a quantity of protrusion thereof from supports 805a and 805b. The supports 805a and 805b have end portions fixed to an alumina ceramic disc 807 and are electrically insulated from each other. The supports 805a and 805b have leg portions that are electrically in contact with electricity introduction terminals 808a and 808b, respectively, and with application of electric current of several amperes, the pyrolytic graphite members 802a and 802b are heated to maintain the single crystal chip 801 of LaB6 or CeB6 at a high temperature of about 1500° C., thereby allowing the single crystal chip 801 to operate as a thermal electron gun cathode or a thermal field emission cathode.
The Vogel mount type electron gun cathode described above, which is formed of an LaB6 or CeB6 single crystal chip fixed by two pyrolytic graphite members on the respective sides with springs, has a disadvantage that the structure of the electron gun cathode is complicated, which makes alignment of the central axis of electrons relatively difficult. Another disadvantage is that, because heating is performed by electric current, in the case of manufacturing a high voltage source for a multi-column device having, for example, several tens of columns, a circuit for generating a large amount of electric current of a total of several tens to several hundreds of amperes for a high voltage source of several tens of kV (e.g, about −50 kV) is mounted, which results in an increase in the capacity of the high voltage source. Further, in order to transmit electric current of several amperes to individual electron guns, an electric wire line having a diameter of several millimeters or greater, for example, is necessary, and, in consideration of high voltage insulation, the wire lines must be covered with an insulating material such as a rubber, which will increase the diameter of the wire line to at least about 10 mm or greater. As such, several tens or more electric wire lines whose diameters are thus doubled because of heating by electric current are necessary, forming a power source cable having a cross section with a diameter of about ten and several centimeters. Consequently, as mechanical vibrations are propagated from the power source cable to the multi-column mounted on a vibration-preventing stand, it is not possible to draw a pattern with accuracy of 1 nm or less.
Patent Documents 1 and 2 disclose technology for radiating laser light in a non-contact manner from a front surface side or a back surface side of the tip portion of the electron gun cathode material to thereby effectively heat the electron gun cathode, thereby extracting a large quantity of electron beams.